It is known that the IV characteristic, which shows characteristic of electric power generation of a fuel cell, changes with temperature of the fuel cell. Accordingly, the IV characteristic of the fuel cell can be obtained by measuring temperature of the fuel cell. However, temperature of the fuel cell changes depending on the position at which the measurement is made as well as on the wet condition thereof; and thus, it is difficult to know accurately the IV characteristic of the fuel cell only by the measured temperature.
In JP2000-357526A, a method is disclosed with which the IV characteristic is estimated based on the detected values of the electric current and voltage of the fuel cell.
In JP2000-357526A, the load to which the electric power is supplied from the fuel cell is controlled thereby changing the electric current taken out from the fuel cell, and the IV characteristic is estimated from the relationship between the voltage of the fuel cell at this time and the electric current taken out therefrom.